MECHANICAL SEPARATION 319
compressed to 35 Ib. per square inch. Repairs about the filter in 2 years time have been very slight. The power required to run the installation is estimated at 20 hp. and 6.7 Ib. of zinc oxide are recovered per minute.
The entering dust-laden air has to make a turn before passing through the bags, this assists in dropping out any large particles which would tend to cut the bag fabric.
Stocking Dust Collectors.—These are manufactured by most of the manufacturers of grain-cleaning and flour-milling machinery. The general form of these machines is illustrated by Fig. 35 with a body made of galvanized iron. The dust-laden air enters at A and is first given a centrifugal whirl to separate out any coarse particles or abrasive particles tending to cut the cloth of the stockings. The latter are arranged around the center of the separator and are secured to a center rotating drum. When the stockings come over the hopper
FIG. 35.—Stocking dust collector.
portion of the case means are provided for shaking and discharging them. For each square inch of fan opening the following number of square feet of filtering cloth is required: Receiving separators and corn cleaners 3 sq. ft.; milling separators 2J£ sq. ft.; scourers 3 sq. ft.; oat clippers, 4 sq. ft., purifiers, 7 sq. ft. For roll suction for each double stand of four rolls, 6X12, 25 sq. ft. up to 50 sq. ft. for 10 by 36. The principal advantage of the stocking filter is that material dropping into the hopper may be withdrawn without interfering with the separation.
The Cottrell Process.—The Cottrell process is a separation by the silent or glow discharge from high-voltage direct current. The electrodes are usually a small pipe about 10 ft. long and 6 in. diam. through the center line of which is